The present invention relates to high surface area micro-porous fibers made from polymer solutions, and particularly high surface area fibers for filtration application where surface micro-cavities are used to retain solid and/or liquid reagents for selective filtration to reduce certain smoke components.
Current cellulose acetate (CA) fibers used in cigarette filters are made by a dry spinning process which allows a 20-25% acetone solution of CA to be pulled or squeezed through the bottom holes of spinerettes or jets, and slowly shrunken into final fiber form by removing acetone solvent in a long spinning column approximately 5-10 meters long. Dried with a pressurized hot air stream in the column, the thus formed fibers with cross-sections such as xe2x80x9cRxe2x80x9d, xe2x80x9cIxe2x80x9d, xe2x80x9cYxe2x80x9d, and xe2x80x9cXxe2x80x9d depending on the shape of the holes through which they are pulled or squeezed have a continuous core cross-section and relatively limited outer surface areas because of the heat involved.
Accordingly, it is an object of the present invention to increase the outer surface area of certain fibers made from polymer solutions by forming micro-cavities useful for retaining solid and/or liquid reagents for selective filtration in the reduction of certain smoke components in tobacco products such as cigarettes.
Another object of the present invention is a process for producing high surface area fibers for filtration application in tobacco products such as cigarettes.
Still another object of the present invention is a process of producing high surface area fibers from polymer solutions where micro-cavities on the fiber surface are used to retain solid and/or liquid reagents for selective filtration in the reduction of certain smoke components in tobacco products.
In accordance with the present invention, a polymer solution is allowed to pull through the spinneret of a dry spinning process. A rapid evaporating process at reduced pressure is applied to the initial form of the fibers after a certain degree of drying in air-spinning columns where a dried skin of polymer is formed on the fiber surface. A residual amount of solvent or a blowing agent inside this skin explodes or pops and quickly leaves the fiber through various micro-porous paths under reduced pressure, leaving behind high surface area fibers with micro-porous cavities and internal void volume. For cellulose acetate fibers, an evaporating temperature below 60xc2x0 C. in the evaporating process is essential in order to preserve the thus formed micro-pores in the fiber surfaces.
The process can be extended to polymer materials other than cellulose acetate as well as solvents and so called popping agents other than acetone. Also, suitable fibers are fibers from a melt polymer dope with air trapped in a chilled hard outer skin. The low temperature evaporation process can be applied in an on-line or in a batch manner.